STUDIES ON SULFATIDES BY QUADRUPOLE ION-TRAP MASS SPECTRMETRY WITH ELECTROSPRAY

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The structural characterization of sulfatides by collisional-activated dissoctiation (CAD) quadrupole ion-trap tandem mass spectrometric methods with electrospray ionization is described. When subjected to CAD in the negative-ion mode, the [M - H](-) ions of sulfatides yield abundant structurally informative ions that permit unequivocal assisgmensts of the long-chain base, and fatty acid constituent including the location of double bond. The identification of the position of the double bond on the fatty acyl substitute is based on the observation of the series of the ions arising from classical charge-remote fragmentation processes similar to those observied by high-energy CAD and by tandem quadrupole mass spectrometry. An unusual internal galactose residue due to a rearrangement process was also observed. The [M - H](-) ions of sulfatides also dissociates to a ceramide anion, which undergoes consecutive fragmentation porcesses to yield ions informative for identification of teh ceramide moiety and premits distinction the sulfatide with a sphingosine subclass from that with a sphinganine long-chain base subclass. The MS(2)-spectra of the sulfatide subclass with a spingosine LCB and a alpha-hydroxy fatty acyl substituent (d18:1/hFA-sulfatide) are featured by the prominent ion sets of m/z568, 550, 540 and 522, originated from a primary cleavage of the fatty acyl CO CH(OH) bond, and are readily differentiable from those arising from the non-hydroxy sulfatide subclass (d18:1/nFA-sulfatide), in which the ion sets are low abundance. The fragmentation pathways of sulfatides under low-energy CAD are proposed. The pathways are supported by the MS- and MS-spectra of various compounds, and of their H-D exchanged analogs.